1. Field of the Invention
The present invention is directed to using offset correction to lower noise in a transimpedance stage of an amplifier.
2. Background Art
Transimpedance amplifiers (TIAs) and limiting amplifiers (LAs) are typically used in optical receivers, and other devices. The are positioned at front end stages of a system to convert current from a detector (e.g., a photodetector) to voltage output, which is then fed to a clock and data recovery (CDR) circuit. TIAs in high speed communications (e.g., 10 GHz/s baud rates) are often faced with stringent requirements for reducing the input referred noise. This is needed to maximize the signal-to-noise ratio (SNR) of the TIAs. This results in lower bit error rates (BERs) when the TIAs are used in optical receiving devices (e.g., photodetectors, optical sensors, optical detectors, or the like). Often, the limiting amplifier (LA) receives a signal from the TIA to limit a signal generated by the TIA before the signal is sent into the clock and data recovery circuit (CDR). In other cases, TIA's themselves can be implemented as a transimpedance first stage followed by one or more amplifier stages. Usually, a feedback device is positioned between an output of the TIA and an input of the transimpedance first stage of the TIA to generate a feedback signal that removes unidirectional currents D.C. offset or any other D.C. offset that exists in all the stages of the amplifier. Unfortunately, the feedback device results in additional noise in the design of the transimpedance amplifier.
Therefore, what is needed is an improved topology for a transimpedance first stage, which can reduce noise in the TLA to an acceptable level. What is also needed other mechanisms to reduce noise specifically in the first stage of the transimpedance stage, which contribute a significant part of the overall noise.